In severe unilateral disease considerable advantage is gained if the two lungs can be ventilated independently in proportion to the gas exchange of each lung. Perhaps many patients with diffuse disease may also benefit from differential lung ventilation. After developing a microprocessor controller for differential ventilation, we will conduct a study of the therapeutic modalities of differential lung ventilation during unilateral lung disease and then investigate differential ventilation for the treatment of diffuse ARDS with differential PEEP and asynchronous ventilation.